1. Field of the Invention
The present invention deals with the composition, and application of novel alkoxylated amido sulfates, useful as surface active agents. Compounds of this invention have foaming, emulsification, wetting, softening, anti-tangle, and conditioning properties. They also exhibit an ability to emulsify larger quantities of oil and other hydrophobic materials than standard emulsifiers.
2. Description of the Art Practices
The nature and structure of the amido group in the molecules of the present invention are of major significance to the novel functional attributes of the compounds of the invention. This novel structure comes from the synthetic route used to make the novel alkanolamides. Traditional alkanolamides have been known for many years and have been widely used in many market segments as foam boosters, emulsifiers, antistats and corrosion inhibitors. Chemically, these alkanolamides are the reaction product of an alkanolamine and a fatty material. Fatty materials are a class of compounds which include fatty carboxylic acids, fatty methyl esters and fatty glycerides (also called oils). The source of the fatty materials include coconut, peanut, soybean, and rapeseed oils, fractionated and non-fractionated fatty methyl esters and acids of almost any carbon length.
U.S. Pat. No. 2,089,212 to Kritchevsky issued August 1937, details the production of fatty alkanolamides from ethanolamines and fatty acids. U.S. Pat. No. 2,094,609, to Mead details the development of the conventional alkanolamide process to make products derived from fatty esters and glycerides.
Despite their wide use and commercial acceptance, alkanolamides have had some short comings. They are generally used in combination with a foaming agent like sodium lauryl sulfate to provide foam stabilization. There are significant practical limitations in the range of applicability of these materials as truly multi-functional surface active agents. The reason for this is that the variables which can be altered in traditional alkanolamide chemistry is limited to the choice of fatty material and the choice of alkanolamine. This molecular limitation results in limitations on properties obtainable in alkanolamides (for example, alkanolamides are seldom used as primary foamers).
In addition traditional alkanolamides have come under suspicion for containing nitrosamines, which are potent cancer causing agents. The nitrosamine is formed by an undesirable side reaction of the alkanolamine. There have been recent efforts by industry to keep the free alkanolamine level present in alkanolamides as low as possible to minimize the concentration of nitrosamines. This approach has met with limited success since the alkanolamide is in equilibrium with several reactive species. Consequently, the preparation of an alkanolamine free alkanolamide using conventional amide technology is highly questionable.
Fatty alcohol sulfates and more recently fatty alcohol ether sulfates have been known for many years and are the workhorse of the personal care industry. While the former is an excellent detergent, the latter class of materials have become a factor in recent years because of the consumer's desire for low irritation personal care products. Selection of the correct sulfate is another complication. With any given molecule, there is a trade off between detergency and lower irritation. Higher molecular weight alcohols generally give less irritating sulfates, however the higher molecular weight species are generally solid. Sulfation of solid alcohols (i.e. those linear compounds with more than 16 carbons) represents several technical and production problems. The higher temperatures of sulfation and paste nature of the finished products represents a major draw back. One other option to get less irritating sulfates is to add ethylene oxide. Sodium laureth 5 mole ethoxylate sulfate is much less irritating than sodium lauryl sulfate, however the added ethylene oxide makes it more water soluble and consequently it is not a good detergent. Lastly, incorporation of an amido function into a surface active molecule is a commonly used method to lower irritation. Cocobetaine is much more irritating than cocamidopropylbetaine. Alkanolamide based ether sulfates are known and enjoy some sales, although their popularity when compared to ether sulfates is quite low. This type of material are typically based upon the reaction of a cocomonoethanolamide or an ethoxylated coco- monoalkanol amide with a suitable sulfating agent using procedures known to those skilled in the art. The products of this reaction are good lime soap dispersants and show some additional surface active properties. A major problem encountered with the sulfated ethanolamides is hydrolysis. The sulfate group is positioned in such a way that the hydrolysis occurs by an energetically favored 6 member ring transition molecule. Compounds of the present invention have the nitrogen and carboxyl group in the compound reversed so that there is no six member transition state possible. As will become apparent later this results in significantly improved alkaline stability.
U.S. Pat. No. 3,5622,170 issued in 1971 to Zorayam teaches that some of the hydrolytic instability can be overcome by using a diglycolamine based alkanolamide in synthesis of a sulfate. While this advance gives some increased stability, it is not as effective as the reversal of the position of the carboxyl (C.dbd.O) function and the amine group (NH) disclosed by this invention.